@Enriador, Octavius and Strider:
That's what i tried to sideway speak about further above ... an App i think would not add much over a mobile-ready web interface for the existing players, exept better notifications (but it may be a disadvantage then to classic players who don't get reminders or message notifications, making them slower). But an App could draw new folks that don't look for games on the internet anymore, but on the app stores. Hard to make that all practically happen though with the ressources available.
Anyway, a web interface that actually behaves well on mobiles would be a big step. Currently it's scaling, zooming, scrolling etc. That's doable for players highly involved who want not to miss a turn while on the move, but it's all but attractive for new players to start. Saying you have to use a real computer to really play the game just scares them away too – the negotiations part that is a primary aspect of this game is hard enough on a mobile (but improving too), the rest should not.
Even not considering proper mobile browsers support, the interface and design on a classic computers, while it is functional and totally okay to regular players, it is not appealing to new folks. Filling out forms in browser games is so year 2000, it aestetically looks like Web 1.0, and the whole interface is not very intuitive to new players. I tried to recruit some people over the years to join the game that i enjoy to play that much – with some i succeeded, but some just didn't overcome the first impression and problems they had.
I completely understand it's a grown interface that was extended with features now and then, and that's totally okay, but there's missing an overal concept of information and fucntions hierachy and bunding, questioning features, re-thinking features, add features, etc.
That should not sound destructive, i can for myself go on and play with that interface for many years without pain, but with a professional perspective of an interface designer, and also from a perspective of a newcomer to play on the platform, there are severe user experience problems and hurdles put in the way of players interested to play this great game. This also is not specific to vdiplomacy, it's the same for webdiplomacy and other forks too (i don't know any other platforms and how they are better or worse).
Again, question is what can be done and who is in power to do it ... i can provide thoughts, advise and web frontend code if wanted, but as this is lots of work to do when done right, the organisational structure of such a project would have to be defined. It's more than just fiddling around with ideas like in the link above.